About 24-hours later, Jackson stood over the lifeless body of a woman in his battalion — the death a result, a forensic psychologist testified, of a potent combination of alcohol and anti-depressant pills.

Whether Jackson intended to kill Spc. Brandy Fonteneaux in January dominated testimony in the sergeant’s court-martial on Tuesday, when the Army prosecutors that charged him with premeditated murder turned the case over to his defense attorneys.

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Jackson allegedly said he walked into Fonteneaux’s room, woke her and began stabbing — inflicting dozens of cuts and stab wounds before strangling her as she lay gasping for air, his best friend, Christopher Coulston, testified on Tuesday.

Shortly before the killing, Jackson was cleared for retirement by a medical board, witnesses said. Jackson suffered a shrapnel wound in Afghanistan.

Declaring Jackson’s mental state the “point of this trial,” Capt. Jeremy Horn, a defense attorney, focused largely on testimony from Gail Poyner. The Oklahoma City-based forensic psychologist quoted studies and research on the anti-depressant Jackson consumed that night, along with at least two-thirds of a bottle of Crown Royal whiskey.

“I strongly believe that Celexa is the approximate cause of this crime,” Poyner said.

She testified after prosecutors relentlessly questioned her credentials. She has a doctorate in psychology from the University of Oklahoma, but Poyner said she isn’t certified through several trade associations, including the American Board of Forensic Psychology.

Prosecutors also questioned her lack of schooling in biology, chemistry and physiology after she received her associates degree. She said it wasn’t a requirement.

The court-martial recessed for the day before prosecutors could cross examine her.

Earlier Tuesday, Capt. Jason Quinn, a prosecutor, called his last witness — a former soldier who spoke of the conversation he had with Jackson while the two smoked cigarettes one day before the killing.

When asked by Jackson how he’d kill someone, Nryk Stewart said he’d use a gun. The answer confused Jackson, Stewart testified.